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Full text of "Treatise On Applied Analytical Chemistry(Vol-1)"

WHITE  METAL

261

For each group the method of analysis will be described later, but
since for certain purposes only the content of copper or tin is of interest,
a general method is given which permits of the direct and moderately rapid
determination of each of these elements.

1.  Direct Determination of the Copper.1—In a 200 c.c. measuring
flask, 5 grams of the alloy are heated gently with 20-25 c-c- of nitric acid
(D 1-2) *  when the action is complete, the nitrous vapours are eliminated
by short boiling and the liquid cooled, treated with 3 c.c. of cone, sulphuric
acid, again cooled, diluted somewhat, rendered alkaline with ammonia,
treated with 15-20 c.c. of 10% sodium phosphate solution and made up
to volume and mixed.    After standing, the liquid is filtered through a
dry filter and 100 c.c. of the filtrate neutralised with nitric acid, treated
with 6 c.c. of cone, nitric acid and 20 c.c. of 10% sulphuric acid, and elec-
trolysed :   Winkler cathode }   spiral Winkler  anode ;   ND100 = 0-2 amp. ;
voltage = 1-8-2-2 ; and duration, 10-12 hours.

When the copper is completely deposited, the electrolytic beaker is
replaced by another small beaker full of distilled water acidified slightly
with sulphuric acid, the cathode being detached after some time, washed
with water, alcohol and ether, dried at 70° and weighed. (Weight of coppe:
found) X 40 = percentage of copper in the sample.

If the alloy contains arsenic, the copper deposited may have a brown
colour. In this case the deposit is dissolved in 5-6 c.c. of nitric acid and
the liquid diluted and again electrolysed.

2.  Direct Determination  of the Tin.—According to the supposed
tin content, 1-3 grams of the alloy in fine filings are treated with 15-20 c.c.
of concentrated, boiling sulphuric acid, the subsequent procedure being
that indicated for the direct determination of tin in hard lead (seep, 247).

1. Alloys with a Tin-Antimony Basis

These alloys usually contain 70-85% Sn, 10-15% Sb, 5-10% Cu, 0-5-
2 % Pb, with possibly zinc and iron. Their complete analysis is carried out
as follows :

A. Electrolytically.2—In a conical flask covered with a small funnel,
0-5-1 gram of the alloy in turnings or filings is treated with the least possible
quantity of aqua regia (10-15 c.c.). When the action is over, 10-15 c.c.
of water containing in solution 2—3 grams of tartaric acid are added and
the liquid made slightly alkaline with concentrated caustic soda solution
and treated with a further quantity of 2 grams of sodium hydroxide and
10-15 c-c- °t sodium sulphide solution (D 1-225). The liquid is heated on
a water-bath with frequent shaking and after about 15 minutes—when
the sulphides insoluble in sodium sulphide have settled—filtered by decan-
tation through a filter moistened with sodium sulphide into a tared Classen
dish. The residue is washed by decantation five or six times with tepid
sodium sulphide (70-80 c.c. in all) and then once with a very little hot
water containing a few drops of sodium sulphide. The filtrate contains

1  Belasio :   Ann. Labor. Chim. Gabette, VI, p. 284.

2  Belasio:   Ann. Labor. Chim. Gabelle, VI, p. 217.imony present is calculated as tin,